Error correcting codes are widely utilized in wireless communications. Error-correcting codes compensate for any intrinsic unreliability of transmitted information by introducing redundancy into a data stream. Considerable interest has recently grown in a class of codes known as low-density parity-check (LDPC) codes. LDPC codes have been demonstrated to provide error-rate performance close to channel capacity, which represents a lower bound for wireless transmissions.
Encoding of LDPC codes refers to a procedure that produces a codeword from a set of information bits by incorporating a certain number of redundant bits called parity bits. Rate of an LDPC code is defined as a ratio of a number of information bits and a total number of encoded bits (i.e. information bits and parity bits).
Emerging communication standards continuously evolve and they are required to operate under various channel conditions retaining high performance over a large range of time varying noise levels. A method that is frequently employed to achieve reliable and consistent transmission in communications systems is the use of forward error-correcting (FEC) schemes supporting variable code rates, thus ensuring high system performance in all operating modes. It is of particular interest that one single FEC scheme can operate, or support, a wide range of code rates, spanning from extremely low code rates (e.g., 1/5) for extremely low quality channel conditions, up to quite high rates (e.g. 9/10) for certain good quality channel conditions, in a consistent, hardware friendly manner, with minimal loss in overall system's performance.
There is a need for improved techniques for constructing LDPC codes capable of supporting multi-rate encoding across a range of code rates, from low to high, and which do not require significant computational complexity.